The invention relates to a process for preparing functionalized thermoplastic elastomers based on graft substrates selected from                olefin block copolymers having the composition from 80 to 98 mass-% of ethylene-12 to 20 mass-% of C3- to C12 olefin units, or        semi-crystalline propylene/ethylene and/or C4- to C12 olefin copolymers and/or C4- to C12 diene copolymers of the composition 50 to 98 mass-% of propylene-/2 to 50 mass-% of C2- and/or C4- to C12-olefin units and/or C4- to C12-diene units, or        cross-linked styrene/olefin/styrene- or styrene/olefin-block copolymers.        
For numerous applications, particularly as compatibility or adhesion promoter (adhesive agent), statistical (random) and heterophasic (impact) propylene copolymers (RCP, HCP), ethylene/propylene copolymers (EPM) or ethylene/propylene/diene terpolymers (EPDM) containing carboxylated olefin polymers based on polyethylenes of different density (LDPE, MDPE, HDPE), ethylene/α,β-ethylenically unsaturated C3- to C12 olefin copolymers (LLDPE, POE) or propylene-homo (HPP) and C2- and/or C4- to C12 olefin units are used. The aforementioned polymers are generally produced by means of reactive extrusion at high temperatures (150 to 300° C.) by grafting on the olefin backbone polymer an α,β-ethylenically unsaturated mono- or dicarboxylic acid or the anhydride thereof, particularly methacrylic acid, fumaric acid, and preferably maleic anhydride (MA), in the presence of a free-radical-forming peroxidic initiator.
The above-described prior art can be found, inter alia, in the WO 91/18053 A1, U.S. Pat. No. 4,174,358 A, U.S. Pat. No. 4,537,929 A, U.S. Pat. No. 4,684,576 A, U.S. Pat. No. 4,751,270 A, U.S. Pat. No. 4,927,888 A, EP 0 266 221 B1, EP 0 287 140 B1, EP 0 403 109 A2, EP 0 467 178 B1, EP 0 581 360 B1, EP 0 696 303 B1, EP 0 878 510 B1, U.S. Pat. No. 6,884,850 B2, US 2006/0211825 A1 and WO 2008/079784 A2.
In the same way, the corresponding functionalized olefin polymers are obtained by grafting α,β-ethylenically unsaturated compounds containing hydroxyl, epoxy, amino, imido, silane groups and other functional groups.
Increasingly, highly effective, non-cross-linked olefin elastomers composed of predominantly ethylene and/or propylene units produced by using special metallocene catalyst systems or random copolymers containing predominantly isotactic propylene sequences and about 8 to 32 mole % ethylene units are used as backbone polymers for functionalizing monomers having functional groups by grafting (functional monomers). The non-cross-linked olefin elastomers include especially ethylene-α-olefin block copolymers, such as the Infuse™ types from Dow Chemical Company. Examples for the random copolymers containing about 8 to 32 mole % ethylene units are the Vistamaxx™ types described in the documents U.S. Pat. No. 6,884,850 B2, US 2005/0176888 A1, US 2006/0199930 A1 and US 2006/0211825 A1 from ExxonMobil Chemical Company or the Versify® types from Dow as well as Notio™ types. The aforementioned types of ethylene-α-olefin block copolymers and random copolymers from the Dow Chemical Company are described in the documents US 2006/0199914 A1, WO 2006/102016 A2 and WO 2008/080111 A1. The employed functional groups include, among others, carboxyl- or anhydride-, as well as hydroxyl- or epoxy-, amino-, imido- or silane-groups. The employed monomers with functional groups particularly frequently include α,β-ethylenically unsaturated mono- or dicarboxylic acids or their anhydrides (carboxyl monomers), for example, maleic anhydride.
Graft-carboxylation or graft-maleation performed at low reaction temperatures, i.e. below the melting or softening point of the olefin backbone polymer (graft substrate) in a solvent is, due to the technologically very complex polymer dissolution and in particular due to the solvent separation and solvent recovery necessary and the required graft product purification after grafting, not an economic alternative to the melt-grafting of acid (anhydride)- or other functional monomers on graft substrates composed of predominantly olefin units. Conversely, the functionalization of olefin polymers carried out in a solid-fluid polymer phase, particularly a carboxylation or maleation, are based on an economic technology study carried out below the melting or softening temperature of the graft substrate. This is known from the documents DD 275 160 A3, DD 275 161 A3, DD 300 977 A7, DE 41 23 972 A1, DE 43 42 605 A1, EP 0 469 693 B1 and EP 0 370 753 B1.
Suitable backbone polymers for this graft-functionalization (solid state grafting) carried out in the solid phase are semi-crystalline olefin polymers, which allow high diffusion rates of low molecular weight compounds in the amorphous phase formed between its glass-transition and melting point, with unsaturated carboxylic acids or anhydrides being among the low molecular weight compounds. High diffusion rates for low molecular weight compounds are one of the prerequisites for high graft-polymerization velocities.
Amorphous and low-crystalline olefin elastomers with special morphology, in particular elastomeric olefin segments containing styrene/selectively hydrogenated diene/(styrene) multi-block copolymers, can also be used as the polymer backbone for the free-radical solid-phase graft modification under certain polymerization conditions, see documents EP 0 642 538 B1, EP 0 805 827 B1 and WO 2004/048426 A2, without achieving the required properties for use as a highly effective adhesives, including adhesion promoters for demanding metal/plastic and other multi-layer composites.
Frequently used adhesion promoters include, besides carboxylated or maleated high-density polyethylenes with the abbreviation HDPE, or carboxylated branched low-density polyethylenes, with the abbreviation LDPE, especially low-density carboxylated linear ethylene copolymers, furthermore random propylene/ethylene copolymers composed predominantly of propylene units and lastly also styrene/selectively hydrogenated diene segment/styrene or styrene/selectively hydrogenated diene segment block copolymers, with the abbreviation TPE-S, containing “elastomeric” olefin units, which are the purpose of their carbonation, especially maleation, produced mostly by melt grafting, as described, for example, in the publications U.S. Pat. No. 5,346,963 A, U.S. Pat. No. 6,384,139 B1, U.S. Pat. No. 6,331,592 B1, U.S. Pat. No. 6,884,850 B2, DE 198 41 303 A1, WO 01/92357 A1, WO 98/42760 A1, EP 0 659 784 B1, U.S. Pat. No. 4,578,829 A, EP 0 173 380 A1, EP 0 085 115 B1, EP 0 371 001 B1 and EP 0 642 538 B1, and which can be used as adhesives for various applications, as disclosed in the documents EP 0 696 303 B1, EP 0 754 731 B1 and EP 0 878 510 B1. The carboxylated linear ethylene copolymers either have a low C3- to C12-olefin co-monomer fraction below 15 mass-%, i.e. LLDPE, or a higher C3- to C12-olefin co-monomer fraction above 15 mass-%, referred to by the acronym POE. Carboxylated linear ethylene copolymers include, for example, special ethylene/octene (C8) copolymers, referred to by the acronym EOC.
Moreover, bonding resins using mixtures of crystalline polyolefin, for example HDPE or LLDPE, and an amorphous or poorly crystalline olefin polymer, for example ethylene/propylene rubber with the abbreviation EPM, that were graft-carboxylated in the melt, are known and described in the publication EP 0 501 762 B1.
The known melt-grafted olefin thermoplastic elastomers disadvantageously have low levels of bonded functional groups. A low grafted functional monomer fraction is thus present, i.e. a low degree of functionalization. Another drawback is the technical/technological and expensive measures for the removal of the high residual monomer fractions from the melt.
A process for preparing functionalized polypropylenes with polypropylene by radical grafting with low molecular weight compounds having functional groups under solid phase reaction conditions is known from DE 199 14 146 A1. In this process, the grafting of compounds having functional groups on polypropylene is carried out by continuously feeding the reactants and by continuously removing the reaction product in the temperature range between 80 and 160° C. The method is used, among other things, to improve the adhesion of polypropylene to mineral reinforcing materials.
DE 10 2007 030 801 A1 describes thermoplastically processable carboxylated styrene-olefin block copolymer/polyolefin compositions with a melt volume rate of MVR (230° C./5 kg) between 1 to 300 cm3/10 min and a fraction of grafted α,β-olefinally unsaturated mono- and/or dicarboxylic acid and/or of its anhydride in proportion to the entire polymer mass of between 0.3 and 5 mass-%. The melt-processable carboxylated styrene-olefin block copolymer/polyolefin compositions can be used as an adhesion promoter in coatings on different surfaces, in laminates and composites.
DE 196 07 430 C1 discloses a continuous process for the modification of polyolefins in the solid phase. The modified polyolefins, for example styrene-modified polypropylene, can be prepared by a continuous process in which unsaturated monomers and thermally decomposing radical formers are absorbed from the gas phase by using polyolefin particles, and wherein the polyolefin particles in which the thermally decomposing free-radical generators and unsaturated monomers are absorbed, are exposed to a high-frequency field having a frequency of 2.4 to 2.5 GHz. The modified polyolefins are suitable for producing films, sheets, coatings, pipes, hollow bodies, foams and molded materials.
A method producing carboxylated ethylene polymer blends is known from WO 2009/033465 A2. In a first stage 0.05 to 15 mass parts of an α,β-ethylenically unsaturated mono- and/or dicarboxylic acid or its anhydride, or a monomer mixture containing at least one monomer and 0.01 to 10 mass parts of a radical initiator mixture are added to 100 mass parts of an ethylene polymer selected from ethylene-homo and/or linear ethylene copolymers, and graft-polymerized at reaction temperatures between 30 and 120° C. for a reaction time between 5 and 120 min. In a second stage, a mixture of 100 mass parts of the modified ethylene polymer obtained in the first solid phase stage, 150-4000 mass parts of an ethylene polymer- or polymer blend, and 150-4000 mass parts of an olefin elastomer are continuously fed to a reaction extruder, reacted at temperatures of between 160° and 260° C., wherein the graft-modified ethylene polymer blend having a degree of carboxylation between 0.05 and 1 mass-% is then continuously discharged. These products obtained on the basis of ethylene-homo and/or linear ethylene copolymers products are intended, inter alia, for use as adhesion promoters.